An attempt will be made to identify the factor(s) in the cytosol from livers of fed chicks which retards the dissociation and stimulates the catalytic activity of fatty acid synthetase complex from livers of starved chicks. In addition, an investigation of the pheonomenon of rapid return of fatty acid synthetase activity that occurs upon refeeding of starved chicks will be made. Cycloheximide does not prevent the initial response of the enzyme to refeeding and therefore, the incorporation of C14-labeled leucine into fatty acid synthetase protein during starvation and refeeding (with and without cycloheximide) will be studied. In these same experiments, attempts will be made to quantitate the amounts of fatty acid synthetase protein by preparing antiserum to purified enzyme and using the antiserum to quantitate the enzyme in experimental tissues by immunodiffusion techniques.